Air and exhaust gas management system for a two-cycle internal combustion engine

ABSTRACT

The air and exhaust gas management (scavenging) system for a two-cycle internal combustion engine allows the engine to perform comparably to similar four-cycle engines, while remaining lighter, simpler and more cost-effective than its four-cycle counterpart. Scavenging is achieved by locating at least one and preferably a number of air intake valves ( 1 ) at the top of the cylinder(s) ( 2 ), and at least one and preferably a number of exhaust gas ports ( 51 ) in the lower cylinder walls, in combination with a blower ( 4 ) which drives scavenging air through the cylinder(s) during the piston downstroke once the exhaust gas ports are uncovered.

This application is a 371 of PCT/CA97/00246 filed Apr. 11, 1997 and alsoclaims benefit of U.S. Provisional Nos. 60/019,481 filed Apr. 12, 1996and 60/021,981 filed Jul. 18, 1996.

TECHNICAL FIELD

This invention relates to a two-cycle internal combustion engine, and inparticular, to an improved combustion air supply and exhaust gasdischarge system for same.

BACKGROUND ART

A major problem in the two-cycle engine is the process of purging theexhaust gases and, during the same stroke, providing combustion air.This process of purging the exhaust gases is commonly referred to as“scavenging”. Although fuel injection systems mitigate this problem tosome extent, proper scavenging is indispensable for achieving highefficiency and low exhaust emissions.

DISCLOSURE OF INVENTION

In view of the above, it is an object of the invention to provide an airsupply and exhaust gas management (scavenging) system for two-cycleinternal combustion engines, which allows such engines to performcomparably to similar four-cycle engines, while remaining lighter,simpler and more cost-effective than their four-cycle counterparts.

It is a further object of the invention to provide specific features ofsuch a system, including particular system components and componentconfigurations.

In the invention, scavenging is achieved by locating at least one andpreferably a number of air intake valves in the head of each cylinder,and at least one and preferably a number of exhaust gas dischargeopenings in the lower cylinder walls. The air intake valves arecontrolled solely by air pressure differentials, generated byfluctuating pressure inside the cylinder on one side and in the airsupply chamber on the other side. When the piston rim clears the exhaustopenings on its dowstroke, pressure in the cylinder decreases below thepressure in the air supply chamber, causing the air intake valves toopen and allow scavenging air in. A scavenging blower is used to forceair into the air supply chamber and thence through the valves, in orderto more effectively purge the exhaust gases form the cylinder as thepiston descends. This arrangement can operate in an internal combustionengine utilizing either the Diesel or Otto processes.

The preferred embodiment of the invention is aimed at providing aninternal combustion engine with a potential power output of 100 HP to300 HP, for example, using a modular engine design with, for example, 2,3, 4, or 6 cylinders with displacements of 1.0 L to 3.0 L, as required.The invention is not limited to specific numbers or sizes of cylindersor specific power outputs, however.

Further features of the invention will be described or will becomeapparent in the course of the following detailed description.

BRIEF DESCRIPTION OF DRAWINGS

In order that the invention may be more clearly understood, thepreferred embodiment thereof will now be described in detail by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an embodiment of the invention;

FIG. 2 is a perspective view showing the air supply chamber of thepreferred embodiment, with a multitude of air intake valves arranged inconcentric circles in the cylinder head;

FIG. 3 is a cut-away perspective of the engine block in the area aboveone of the cylinders;

FIG. 4 is a perspective view of one of the check bodies used in theintake valves;

FIG. 5 is a perspective view of an alternative form of check body;

FIG. 6 is a perspective view of another alternative form of check body;

FIG. 7 is a perspective view of an alternative embodiment of the airintake valve assembly, where the valves for each cylinder have beenassembled into a single replaceable unit;

FIG. 8 is a perspective view of the unit of FIG. 7, as seen from thebottom;

FIG. 9 is a cut-away perspective view illustrating the alternative checkbody shapes in the replaceable unit;

FIG. 10 is a cross-sectional view corresponding to FIG. 9;

FIG. 11 is a perspective view of a two-cycle engine, according to theinvention, fitted with the replaceable valve units; and

FIG. 12 is a perspective view showing an exhaust gas oil separatingapparatus which prevents lubrication oil from remaining in the exhaustgases.

BEST MODE FOR CARRYING OUT THE INVENTION

Air Supply Side of the Invention

FIG. 1 schematically shows an embodiment of the invention. Thisembodiment is the currently preferred embodiment, except for the intakevalve configuration. The currently preferred intake valve configurationis a shown in FIGS. 2 and 3, or alternatively as shown in FIGS. 7-10. Asthe development of the engine progresses, other embodiments of theinventive principles may well become preferred to the specific examplesdescribed herein.

In the invention, air intake valves 1, described in detail below,provide passageways between each cylinder 2 and an air supply chamber 3.The air intake valves are activated and controlled solely by airpressure differentials created by fluctuating pressure inside thecylinder on one side of the valves, and in the air supply chamber on theother side of the valves.

A key feature of the invention is that a scavenging blower 4 is providedto purge the exhaust gases and, at the same time, to charge the enginewith air. Depending on the desired characteristics for the engine, thescavenging blower can be a low pressure type which is just able toovercome the resistances of the air and gas flow channels in order toprovide proper scavenging only. Alternatively, a high pressurescavenging blower could be used to provide for pre-compression in thecylinder, for enhanced power output. This high pressure scavengingblower could be coupled with a conventional intercooler 5 to enhance thepre-charging effect.

Because the expansion phase must provide the working stroke in atwo-stroke engine, it is desirable to leave the exhaust ports closed foras much of the downstroke as possible. The use of a blower forscavenging improves performance by permitting the opening of the exhaustports to be delayed without resulting in ineffective scavenging.

The scavenging blower 4 is driven by an electrical servo motor 9 whichallows the scavenging blower to immediately respond to changingoperating conditions of the engine without being dependent on engineoperating conditions such as the revolutions of the crankshaft or theenergy content of the exhaust gas. Accordingly, the scavenging blower isdriven by the servo motor and is controlled, for example, by a computerprogram designed to optimize the function of the scavenging blower. Theservo motor provides the necessary electronic feedback to the computerprogram.

As best shown in FIG. 1, the air drawn into the scavenging blowerpreferably first passes through a conventional air filter 6 and a checkvalve 7. Before the air reaches the three-way diverter valve 8,described in detail below, the air may, for example, pass through aconventional intercooler 5 if increased power output from the engine isdesired.

A three-way diverter valve 8 is located between the intercooler 5 andthe air supply chamber 3. Alternatively, if the engine does not includean intercooler, the three-way diverter valve will be located between theoutlet of the blower 4 and the air supply chamber. The three-waydiverter valve allows more efficient management of the interactionbetween the scavenging blower and the combustion engine.

The three-way diverter valve is linked to the accelerator 10, such thatwhen the accelerator is depressed and full power is called for, thethree-way diverter valve offers unrestricted air flow to the air supplychamber, and when the engine is idling, the air flow is partiallydirected back to the suction side of the scavenging blower.Alternatively, transducers (not shown) for air pressure and air flow maybe incorporated as part of the air supply system to provide feedback tothe electronic control system. In an alternative embodiment, thevariable position of the three-way diverter valve can be controlled by asecond small servo motor (not shown). The control system for this secondservo motor receives feedback from an electronic position encoderconfigured to detect the position of the accelerator.

FIG. 2 shows the air supply chamber 3 with a multitude of identical airintake valves 1 arranged in concentric circles around the top of eachcylinder. The air intake valves penetrate the divider wall 15 in thecylinder head between the air supply chamber and the cylinders. As seenbest in FIG. 3, the air intake valves encircle the combustion chamber 20located at the center of each cylinder.

FIG. 3 also shows that an air intake valve consists of an inlet bore 21with rounded bore edges 22 and an outlet bore 24. In the preferredembodiment, the inlet bore has a diameter of 7 mm and the outlet borehas a diameter of 11 mm. A ring-shaped seat 23 is located in the outletbore adjacent to the inlet bore. A check body 25 floats freely in theoutlet bore and is retained by the seat ring 23 in the up direction andby concentric retainer rings 26 in the downward direction. The checkbody is allowed freedom to move axially away from the ring-shaped seatby a sufficient distance to open a channel to permit air flow. In theclosed position, the check body abuts against the ring-shaped seat,essentially eliminating air flow. The retainer rings concentric to thecylinder axis have a trapezoidal cross-section, and are fitted withingrooves of a complementary trapezoidal shape in the lower plain of thecylinder head. Two bores 27 and 28 penetrate the dividing wall betweenthe air supply chamber and the cylinder to accommodate a spark plug andfuel injection nozzle, respectively.

A check body of various shapes may be sued and is preferablymanufactured from steel, although other materials, such as ceramic andaluminum alloy materials could be used. To provide maximum operatingefficiency, the height of the check body is preferably 8.5 mm and theratio of the drag coefficients of the face adjacent to the inlet boreversus the face away from the inlet bore is 1:4. As shown in FIG. 4, themost effective shape of the check body is a mushroom shape, with asemi-spherical head 30 facing the inlet bore, attached to a conical stem31. The conical stem preferably has a number of holes 32 spaced aroundit, to improve air flow around and through the stem, and to reduce massand inertia. This check body configuration provides for the 1:4 ratio ofdrag co-efficient, as mentioned above, and will insure reliable checkfunctioning when the air intake valve is in the 174 closed position.

Alternative check body shapes may be used, due to cost considerations orfor other reasons. FIG. 5 shows a generally circular disc shape withthree rounded bulges 35. These bulges serve as guiding features to keepthe disc centered within the valve bore, with sufficient radial play,thereby allowing for the axial motion of the check body in the air flowto perform the function of opening and closing the valve. FIG. 6 shows acheck body with the shape of a square disc with rounded corners.Although these shapes do not possess the optimal 1:4 drag coefficientratio discussed above and are, therefore, less suitable aerodynamically,they have the advantage of being able to be mass produced cheaply. Tocompensate for their aerodynamic disadvantage, the scavenging blower,described above, may be adjusted to provide a slightly higher airpressure at no significant extra cost.

FIGS. 7 and 8 show an alternative embodiment of the air intake valveassembly where all of the identical air intake valves for each cylinderhave been assembled into a single replaceable unit 40. The replaceableunit has a tapered circumferential wall 45, which joins the largerbottom face 42 to the smaller top face 43. The replaceable unit containsthreaded bores 27 and 28 to accommodate the spark or glow plug and thefuel injection nozzle respectively. The check bodies are prevented fromfalling out in the downward direction by cross members 41, althoughalternate means of securing the check bodies will be readily apparent tothose skilled in the art.

FIGS. 9 and 10 illustrate the alternative check body shapes which may beused with the replaceable unit. The three different types are shown forpurposes of illustration, but in production only one type would normallybe used in any one unit. FIG. 11 shows a perspective view of a two-cycleengine, according to the invention, fitted with the replaceable units.

Combining all air intake valves for a cylinder into a single replaceableunit is advantageous because the air intake valves are the only parts ofthe cylinder head subjected to wear. Thus, integrating the air intakevalves into a replaceable unit allows for fast and easy replacement ofall of the valves in a cylinder by simply removing the old replaceableunit and replacing it with a new one.

This replaceable unit provides additional advantages. The flattenedlower shape of the cylinder head and the flat, cylindrical shape of thecombustion chamber upon compression assist in facilitating stratifiedcombustion, which is a prerequisite for low toxicity emissions,particularly when the engine is operating in low load mode.

Furthermore, the replaceable unit facilitates changing the compressionratio for the engine, thereby allowing the invention to easily beincorporated into an Otto or Diesel version of a two-stroke engine.

Exhaust Side of the Invention

In addition to locating the air intake valves in the cylinder head, asdescribed above, exhaust gas openings must be located near the bottom ofthe cylinder in order to achieve the straight flow scavenging system. Asdepicted schematically in FIG. 1, exhaust ports 51 are located throughthe lower cylinder walls near the lowest position of the upper pistonrim, when the crankshaft 52 is around the bottom dead center. Theexhaust ports preferably are in the shape of radial slots, although thatis not specifically illustrated in FIG. 1.

When the upper piston rim clears these exhaust ports on the down-stroke,the pressure in the cylinder will decrease below the pressure in the airsupply chamber, causing the air intake valves to open and allow thescavenging air to enter the cylinder. The scavenging air will drive theexhaust gases out of the cylinder via the exhaust ports. Because atleast 50% of a cylinder's circumference remains available for scavengingeven in an engine with more than one cylinder, the height of the exhaustports can be quite small so that, unlike a conventional two-cycleengine, little of the crankshaft angle has to be sacrificed toscavenging. This, in turn, contributes to improved overall engineperformance.

Since the air intake valves are activated by the air flow, which in turnis controlled by the operating conditions of the scavenging blower andthe three-way diverter valve, no exhaust gas recycling valve (EGR) willbe necessary in the engine.

Another positive feature of the invention is the fact that the enginelubrication can be accomplished in the same fashion as in four-cycleengines. This offers freedom of choice in designing the bearings of thecrankshaft and the piston rods without the restrictions posed byconventional two-cycle engines.

Although a two-stroke engine utilizing the system disclosed herein islubricated like a conventional four-stroke engine and does not burn oil,there is a possibility of oil droplets being carried away by the exhaustgases. As the piston 53 is clearing the exhaust ports 51 and thescavenging process begins, the thin oil film on the cylinder walls andon the piston rings may generate tiny droplets of oil that accumulate onthe rims of the exhaust ports. When these droplets grow to a certainsize, they could get torn away by the exiting exhaust gases and enterthe catalytic converter.

FIG. 12 shows an exhaust gas oil separating apparatus which preventslubrication oil form remaining in the exhaust gases and adverselyaffecting the operation of an automobile's catalytic converter. It iscomprised of a spiral housing, either as part of an exhaust gas turbine60 described below, if one is included, or as a separate component. Apart of the outside spiral wall of the housing is interrupted by narrowradial gaps 66 leading from the outside spiral wall into a collectionchamber 64.

According to the invention, any residual oil in the exhaust gas streamis flung against the outer spiral wall and builds up a film which slowlymoves along the spiral wall until it arrives at the radial gaps. Thestatic gas pressure in the spiral housing will drive the oil through thenarrow gaps into the abutting collecting chamber 64. A capillary pipe 65recycles the oil from the collection chamber back to the oil sump (notshown) of the engine.

If the engine is fitted with a conventional turbocharger, the turbinehousing will act as the exhaust gas engine oil separator. If the engineis not fitted with a turbocharger, an empty turbine housing without aturbine wheel will be used.

To partially recover the residual energy of the exhaust gases, thepreferred embodiment depicted schematically in FIG. 1, provides aconventional expansion turbine 60 attached to the exhaust manifoldsurrounding the exhaust ports 51. However, in the preferred embodiment,the expansion turbine is not mechanically linked to the blower part, asin conventional turbocharger. As described above, the scavenging bloweris driven by an electrical servomotor, making the two parts totallyindependent and allowing each to operate optimally in any givenoperating condition. Particularly important is the ability of thescavenging blower to immediately respond the movement of theaccelerator, which eliminates the delay of the increased acceleration ofthe vehicle commonly referred to as “turbo lag”. In the preferredembodiment, the expansion turbine is coupled with the alternator, makingthe conventional battery (not shown) the ultimate energy buffer.

To facilitate the high speed reducing ratio of, preferably, 10:1, thelink between the turbine and the alternator 61 will be realized with amulti-micro profile belt drive (not shown), with a small multi-groovedpulley on the shaft of the turbine and a large pulley (also not shown)on the alternator. Accordingly, the expansion turbine and the scavengingblower are only indirectly linked via the battery and can each workwithin their optimal ranges. Their ability to adapt to changingoperating conditions is more spontaneous than in any conventional directlink combination.

The expansion turbine cannot be the only source of power for thealternator because of its inability to supply sufficient energy to thealternator during periods of underload operation. Therefore, accordingto the invention, the alternator is also lined to the crankshaft, as ina conventional engine, by a second set of pulleys (not shown) andanother drive belt (also not shown), with the diameters of the pulleyssized appropriately for the ranges of revolutions of the alternator andcrankshaft. The two pulleys located on the alternator shaft each possesand integral freewheeling hub 62, allowing the alternator to be drivenby either the expansion turbine or the crankshaft, depending on the loadcondition under which the engine is operating. Preferably, thealternator will be driven by the exhaust gas turbine when the engine isworking at full capacity and maximum power output is required, whereasif the engine is idling, the alternator will be driven by thecrankshaft.

In an alternative embodiment, the freewheeling hubs can be replaced byremotely controlled clutches which are, for example, electromagneticallyagitated. These clutches would allow finely tuned control of the entireair and exhaust gas management system.

The exhaust gas discharge plant 63 is completed by the addition of aconventional catalytic converter and muffler, including sensors todetect the temperature and chemical composition of the exhaust gases.This feedback to the electronic controls is an essential part of theexhaust gas management system.

It will be appreciated that the above description relates to thepreferred embodiment by way of example only. Many variations on theinvention will be obvious to those knowledgeable in the field, and suchobvious variations are within the scope of the invention as describedand claimed, whether or not expressly described herein.

INDUSTRIAL APPLICABILITY

The invention allows a two-cycle engine to arrive at a level ofefficiency, fuel economy, and emission quality of a comparablefour-cycle engine, but with a smaller, simpler, lighter, and moreeconomical power plant.

What is claimed is:
 1. A two-stroke internal combustion engine, havingat least one cylinder with a piston mounted therein for reciprocalmotion between a top position and a bottom position, wherein each saidcylinder has multiple one-way air intake valves above the top of saidcylinder and arranged in any pattern within a single replaceable unit,to allow air into the top of said cylinder, and at least one exhaustport at a lower position just above said bottom position of said piston,and a blower arranged to force air into said cylinder via each saidintake valve as the piston moves around said bottom position, saidblower not supplying enough pressure to keep each said intake valve openduring upward motion of said piston, such that during upward motion ofsaid piston, compression occurs within said cylinder, and such thatduring downward motion of said piston said blower forces air into saidcylinder via each said intake valve once each said exhaust port isuncovered by said downward motion, and out of said cylinder via eachsaid exhaust port.
 2. A two-stroke internal combustion engine as recitedin claim 1, where said air intake valves are controlled solely by airpressure differentials.
 3. A two-stroke internal combustion engine asrecited in claim 1, where said blower is driven by an electrical servomotor which is controlled by computerized control means to optimize itsperformance under different engine operating states.
 4. A two-strokeinternal combustion engine as recited in claim 1, wherein said enginefurther has a three-way diverter valve located between said blower andsaid cylinder(s), said diverter valve being linked to an accelerator,such that when the accelerator is depressed and full power is calledfor, the three-way diverter valve permits unrestricted air flow to saidcylinder(s) and when the engine is idling, the air flow is partiallydirected back to the intake side of the blower.
 5. A two-stroke internalcombustion engine as recited in claim 4, wherein said engine further hasan intercooler connected between said blower and said diverter valve. 6.A two-stroke internal combustion engine as recited in claim 4, wherethree-way diverter valve is controlled by a servo motor which receivesfeedback from an electronic position encoder configured to detect theposition of the accelerator.
 7. A two-stroke internal combustion engineas recited in claim 2, where each said intake valve comprises a checkbody having a ratio of the drag coefficients of its face adjacent to theinlet bore versus its face away from the inlet bore of approximately1:4.
 8. A two-stroke internal combustion engine as recited in claim 1,wherein said engine further has an expansion turbine connected toreceive exhaust from said exhaust port(s) via a passageway, said turbinenot being mechanically linked to said blower, said blower and saidturbine thus operating independently, whereby the operation of each maybe optimized for any given operating condition.
 9. A two-stroke internalcombustion engine as recited in claim 1, wherein said engine further hasan oil-exhaust gas separating means, comprising a spiral housingconnected to receive exhaust gas from said exhaust port(s), said spiralhousing having a plurality of narrow transverse grooves in at least aportion of a wall of said housing on the outside of the spiral, and achamber abutting said grooves for receiving oil therefrom.
 10. Anair-intake valve assembly for use in the head of at least one cylinderin a two-stroke internal combustion engine, wherein said assemblyfurther has: a multitude of air-intake passageways defined in a body,each of said air-intake passageways having an inlet end communicatingwith an air supply chamber and an outlet end communicating with acylinder chamber; and, a plurality of free floating check bodiessandwiched within cavities defined by said outlet ends and retainingmeans, each of said check bodies positionable between an open and closedposition, said positioning controllable via air pressure differentialsbetween said cylinder chamber and said air supply chamber.
 11. Anair-intake valve assembly as defined in claim 12, where said airpressure differentials are controlled by operating conditions of ascavenging blower and a three-way diverter valve means.
 12. Anair-intake valve assembly as defined in claim 10, wherein said assemblyis formed as a single replaceable unit removably attached to thecylinder head.
 13. An air-intake valve assembly as defined in claim 12,wherein said retaining means is a plate mated to a lower end of saidbody having openings shaped so as to retain said check bodies in saidcavities, and wherein said body is further adapted to accommodate aspark or glow plug and a fueled injection nozzle therein.
 14. Anair-intake valve assembly as defined in claim 13, where each of saidcheck bodies has a ratio of a drag coefficients of its face projectingtowards said inlet end versus it face projecting away from said inletend of approximately 1:4.
 15. An air-intake valve assembly as defined inclaim 14, where said blower is driven by an electrical servo motor whichis controlled by computerized control means to optimize its performanceunder different engine operating states.